In the area of mobile electronics technology, there is an increasing demand for more compact, long-life, high energy density batteries. In this regard, there have been lots of researches working to meet the needs. For example, Li-ion battery is currently used for most mobile electronics, and there are extensive researches to improve the battery capabilities. However, because of the theoretical limitation of most secondary batteries, the energy density is low, and the lifetime of the battery still does not satisfy the need of power for mobile electronics. In addition, recharging the battery takes a long time.
In the area of transportation, there is also an increasing demand for more powerful, longer-lasting batteries for emission-free electrically powered vehicles owing to increasing environmental regulations for vehicles. In this regard, there are lots of researches working on hydrogen fuel cells and metal-air batteries. While hydrogen fuel cells are promising, there are still lots of technology challenges, such as methods of hydrogen storage and generation, cost of fuel cell electrodes and proton exchange membrane, etc. Metal-air batteries, in particular, zinc-air battery, also show great potential, because metal-air batteries have a high theoretical specific energy. However, many problems need to be solved for zinc-air battery to be used for transportation application. For example, among other issues as reviewed in U.S. Pat. No. 6,630,262, the methods of recharge of the spent anode still need to be improved in the aspect of convenience, durability, etc.
Separately, U.S. Pat. Nos. 5,804,329 and 6,497,973 disclosed an invention of electroconversion cell using boron redox species, and such electrochemical cells are characterized by favorable features, among others, such as specific energy, recharge efficiency, safety. The patents claims an electrochemical storage medium comprising a carrier mixed with a borohydride compound, the borohydride compound being electrochemically oxidized to an oxidized boron-containing compound concurrent with the generation of an electric current, and the storage medium being in electrical contact with an electrode for carrying current generated during that oxidation. However, it is difficult for such electroconversion cell to achieve the concurrently generating electric current from electrochemical oxidation of borohydride compound. For this reason, this invention did not disclose a detailed effective method to achieve a desired electric current.
Further, the inventor also disclosed high energy density boride batteries in U.S. Pat. Nos. 5,948,558 and 6,468,694. In the patents, reduced boron-containing compound is used as anode to yield an electric current when the reduced boron-containing compound being oxidized to oxidized boron-containing compound during battery discharge. This technology overcomes the difficulty in electroconversion of borohydride as anode material. However, the electroconversion is limited by the solubility of oxidized boron-compound during discharge. Therefore, although the reduced boron-containing compounds are high energy density materials used as anodic medium, the battery still cannot achieve high energy density because of low conversion. In these batteries, halogen compounds, in particular, fluoride, need to be used to increase the solubility of the oxidized boron-compound to achieve high conversion and electric current.
As discussed above, there still exist many technological challenges in prior arts for a battery and/or electric power system with a high energy density and longer lifetime, as well as fast and convenient recharging method. The current invention intends to provide a battery system with high energy density, limited volume, longer lifetime and with a safe, easily recharging methods for the battery system, as electric power sources for mobile electronics and transportation vehicles.